emit an unreachable if an unreachable block context does not end in an unreachable

Author: kripken

src/wasm/wasm-binary.cpp

@@ -583,6 +583,11 @@ void WasmBinaryWriter::recursePossibleBlockContents(Expression* curr) {
   for (auto* child : block->list) {
     recurse(child);
   }
+  if (block->type == unreachable && block->list.back()->type != unreachable) {
+    // similar to in visitBlock, here we could skip emitting the block itself,
+    // but must still end the 'block' (the contents, really) with an unreachable
+    o << int8_t(BinaryConsts::Unreachable);
+  }
 }
 
 void WasmBinaryWriter::visitIf(If *curr) {

test/unit.wast

@@ -537,4 +537,16 @@
     (if (i32.const 1) (nop) (unreachable))
     (if (i32.const 1) (unreachable) (unreachable))
   )
+  (func $unreachable-if-arm
+    (if
+      (i32.const 1)
+      (block
+        (nop)
+      )
+      (block
+        (unreachable)
+        (i32.const 1) ;; ends in a concrete, after an unreachable
+      )
+    )
+  )
 )

test/unit.wast.from-wast

@@ -602,4 +602,16 @@
    (unreachable)
   )
  )
+ (func $unreachable-if-arm (type $FUNCSIG$v)
+  (if
+   (i32.const 1)
+   (block $block
+    (nop)
+   )
+   (block $block12
+    (unreachable)
+    (i32.const 1)
+   )
+  )
+ )
 )

test/unit.wast.fromBinary

@@ -646,5 +646,20 @@
   )
   (unreachable)
  )
+ (func $unreachable-if-arm (type $1)
+  (if
+   (i32.const 1)
+   (block $label$0
+    (nop)
+   )
+   (block $label$1
+    (unreachable)
+    (drop
+     (i32.const 1)
+    )
+    (unreachable)
+   )
+  )
+ )
 )
 

test/unit.wast.fromBinary.noDebugInfo

@@ -646,5 +646,20 @@
   )
   (unreachable)
  )
+ (func $36 (type $1)
+  (if
+   (i32.const 1)
+   (block $label$0
+    (nop)
+   )
+   (block $label$1
+    (unreachable)
+    (drop
+     (i32.const 1)
+    )
+    (unreachable)
+   )
+  )
+ )
 )